Challenge 2 — Solution

Task: Write a function calculateRectangleArea($width, $height = 1) with
a default height of 1, so it can also be used to calculate the area of
a square just by passing one argument. Call it three different ways
and echo each result.

<?php
    function calculateRectangleArea($width, $height = 1) {
        return $width * $height;
    }

    echo calculateRectangleArea(5, 3) . "<br>";   // a real rectangle
    echo calculateRectangleArea(4) . "<br>";      // height defaults to 1
    echo calculateRectangleArea(6, 6) . "<br>";   // a square, given explicitly
?>


Output:
15
4
36

Notes:
- calculateRectangleArea(5, 3) supplies both arguments, so the default
  is never used - the area is simply 5 * 3.
- calculateRectangleArea(4) supplies only $width, so $height falls back
  to its default value of 1 - the area becomes 4 * 1 = 4, which also
  happens to demonstrate that omitting the height doesn't cause an
  error the way it would without a default value.
- calculateRectangleArea(6, 6) shows the same function working equally
  well for a square, just by passing equal width and height explicitly
  rather than relying on the default.